The present invention generally relates to oil and gas exploration techniques, and more particularly to an improved method of data visualization and organization of existing well logs and well log data to identify potential basin-wide depositional characteristics for further exploration and development.
The rocks below us represent a geologic history of the many depositional environments that produced the strata that comprise a basin. Oil and gas knowledge workers have utilized numerous methods for reconstructing the geologic past of a basin to more accurately locate reservoir quality strata. Additional methods have been developed to predict the existence of the hydrocarbons within potential reservoir rocks.
A geologic basin is comprised of hundreds of rock layers or strata (formations) deposited over geologic time that must be understood to predict the location of hydrocarbon bearing rock (reservoirs). Each formation must be analyzed in order to understand and identify the nature of the depositional environment active during its deposition. During a geologic time interval there will be many different types of sediments being deposited. For example, sandstones (a rock composed of sand-sized particles) will be deposited near the point where a river first enters a body of water while shales (a rock composed of very fine-grained particles) will be deposited away from the shorelines in the deeper waters of a basin. A geologic formation may be sandstone in one part of a basin and shale in another. Another important rock type found in basins is limestone, which is composed of calcium carbonate. The dominant rock type in an area of a basin is called a “facies.” Identifying and mapping the change from one facies to another for a particular formation is extremely helpful in predicting the location of reservoir quality rock.
Exploration and development of oil and gas bearing strata in a basin requires the drilling of wells that may penetrate the basin commonly to depths of from 1000 to 29000 feet. Over time, as a basin is probed with many well bores, a large amount of data is generated. One of the data types collected that is used extensively by the present invention is the geophysical well log. These well logs are composed of analog and digital records created when a measuring device is lowered into a well bore and then raised to the surface, all the while recording various physical properties of the strata penetrated by the well bore. This set of records from the well logs will be referred to as “well log data” in the current invention. Well log data as used herein denotes a general term for any data within the well log or extracted from the well log via digitizing, resampling, extrapolation, interpolation, curve fitting etc.
Well logs measure both the induced and ambient electrical and nuclear responses of the strata and other petrophysical properties. Historically, an analog graphical plot was made of the well logs that have a vertical axis representing the depth of the well bore and one or more horizontal axes that represents the amplitude of the measured response. An example of a common well log is the “Gamma-Ray Log” (GR) that measures the natural radioactivity being given off by the minerals in the rocks that compose the strata. The greater the quantity of radioactive minerals in a strata the greater the measured GR response seen on the well log graphical plot. The GR log has proven to be very effective in identifying changes in the geologic strata within a basin.
The knowledge worker in the area of oil and gas development work uses the GR log and other logs for many purposes, including, but not limited to mapping geologic strata, selecting strata to perforate, estimating the original oil and gas in place for a reservoir, and evaluating reservoir quality. The present invention expedites these processes and allows the available well log data to be viewed in ways not previously possible thereby greatly enabling oil and gas exploration and development in a basin.
Identification of the depth at which a particular stratum is penetrated by a well bore is frequently performed using paper copies of well logs. This process is commonly called “correlation”. The common practice today is for the knowledge worker to juxtapose from two to six well logs to correlate the strata in a local area of a basin. Considering that there are tens of thousands of wells drilled in most onshore basins, it is impractical to correlate the hundreds of strata in all wells in a basin without utilizing the present invention.
The present invention takes advantage of a computer's ability to graphically display large numbers of digital well logs simultaneously on a screen to greatly expedite the correlation process and facilitate the correlation of hundreds of strata in all wells in a basin.
Other data besides well logs can play an important role in identifying geologic facies and determining the reservoir characteristics of a given strata. Other data commonly used includes but are not limited to the production history of a well, the well tests, and the core data. The production history typically can include the quantities of oil, gas and water produced from each interval completed in a well. Well tests are records of the types and quantities of fluids recovered from a well bore. Core data record the properties observed or measured for rock recovered from the well bore. The present invention selectively utilizes these data types and any other important or relevant data available in conjunction with the well logs.
The process described in this invention can collect the key information from a plurality of wells in a geologic basin and convert the analog data to digital. Once digital, the oil and gas knowledge worker can interpret the data from many wells much faster than possible without the current invention. Amplification of the digital data is possible to accentuate key features from a given well. The digital data can also be displayed utilizing graphical computerized display tools in an infinite number of variations, which directly leads to an enhanced ability to visualize the strata and production characteristics of reservoirs in a basin.